normals averaging moved to own class

this patch moves the normals averaging of normals connected/stitched meshes out of the BioShapeRenderer class into its own class. Thereby the mesh stitching can happen independently from the BioShapeRenderer.

It works POVRAY and X3d exports but not for OBJ. Did not test for more. It eludes me way it does not work for the OBJ export. The OBJ exporter does something to the meshes but I don't see why the normals change, where they come from.

Best,
Alexander